Utilizing borehole electrical image and conventional logs to characterize petrology of mixed volcanic and sedimentary rocks in Jiamuhe Formation at JL2 Wellfield, Zhongguai Uplift, Junggar Basin, NW China

Abstract

Lower Permian Jiamuhe Formation of JL2 Wellfield, Zhongguai Uplift, Junggar Basin, was constituted by mixed volcanic and sedimentary rocks. The rock types were various, and it is difficult to characterize the petrology just relying on limited cores in oil-bearing intervals. Based on core photos, petrological characteristics were synthetically interpreted using borehole electrical image and conventional logs in this paper. Six types of common volcanic rocks (rhyolite, dacite, andesite, basalt, tuff, and breccia) and three types of clastic sedimentary rocks (conglomerate, sand, and silt-clay) were represented by borehole electrical image log and conventional natural gamma ray (GR), resistivity (RT), neutron (CNL), and bulk density (DEN) logs. Two special volcanic textures, pillow structure and natural fracture, were also described in electrical images. Serial cross-plots in pairs of four conventional logs were formed to distinguish typical rocks, and the distinction between volcanic breccias and sedimentary conglomerates was analyzed in electrical images. Borehole electrical image and conventional logs can be efficiently used to supplement coring and petrological information, which provides important insights on the paleogeology of mixed volcanic and sedimentary rocks in Jiamuhe Formation at JL2 Wellfield.